This invention is related in general to the field of semiconductor devices and processes. More particularly, the invention is related to a system and method for reinforcing a bond pad.
A well known problem area in semiconductor processing is the process of attaching a solder, wire or other bonding elements to a bond pad on a semiconductor integrated circuit. These bond pads are typically disposed above one or more layers or stacks of brittle and/or soft dielectric materials, typically oxides of silicon and some organic materials, for planarization and insulation purposes. Some dielectric materials, such as hydrogen silsesquioxane (HSQ), aerogels, organic polyimides, and parylenes are advantageous for their low dielectric constants compared to silicon oxides, but are weaker structurally and mechanically.
During the bonding process, mechanical loading and ultrasonic stresses applied by the bonding capillary tip to the bond pad often result in fracture of the underlying dielectrics, deformation of the underlying metal structures, and delamination of the layers in the metal structures. These bonding failures may appear as craters in the bond pad and underlying layers as the bonding capillary tip is pulled away from the bonding pad. However, these defects often are not apparent during bonding but would manifest themselves during subsequent bond pull and shear tests, reliability tests such as thermal cyde or thermal shock, or upon deprocessing and cross-sectioning.
Further, weakness of the bond pad structure may also reveal itself during wafer probing prior to bonding. Again, the stresses exerted by the probe tips, typically formed of a hard metal such as tungsten, can cause localized fractures in the pads, despite the fact that then make contact with a soft metal, aluminum, on the bond pads. Such fractures are as much of a reliability hazard as those caused during bonding.
Traditionally, the bonding failures have been addressed by altering bonding parameters, such as ultrasonic power and pulse waveform, bonding temperature, bonding time, clamping force, shape of the bonding capillary tip, etc. Much time is spent experimenting with parameter settings and combinations thereof. Although general guidelines of parameter setpoints and configurations have been developed, the bonding failures persist at a sufficiently significant level to continually threaten the reliability of integrated circuit devices. Yet the failure levels are sufficiently low such that bonding failures become apparent only after several tens of thousands of devices are bonded.
Recent technological advances in semiconductor processing do not alleviate the situation. New dielectric materials with lower dielectric constants are being used to increase circuit speeds but they are mechanically weaker than the conventional plasma enhanced chemical vapor deposition (CVD) dielectrics. Decreasing bond pad dimensions necessitates the increase of vertical bonding force or forces attributable to the use of ultrasonic energy to form effective bonds. Inaccessibility of higher bond parameter settings for fear of damage to the bond pads also results in longer bond formation time, and consequently, lost throughput. All of these significant changes point to a trend of more severe failures and increase in their frequency.
Accordingly, there is a need for a reliable way to prevent or minimize the occurrence of probe and bonding failures where bond pads are situated above one or more structurally and mechanically weak dielectric layers.
In accordance with the present invention, a bond pad reinforcing system and method are provided which eliminate or substantially reduce the disadvantages associated with prior apparatus and methods.
In one aspect of the invention, the reinforcing system for a bond pad according to the teachings of the present invention includes a reinforcing patterned structure disposed in at least one dielectric stack disposed under the bond pad.
In another aspect of the invention, the reinforcing system for a bond pad according to the teachings of the present invention includes at least one dielectric layer or a stack of multiple dielectric layers disposed under the bond pad. A reinforcing patterned structure is disposed in at least one dielectric stack.
In yet another aspect of the invention, a method for reinforcing a bond pad in a semiconductor integrated circuit includes the steps of forming a metal layer, patterning the metal layer in a predetermined area into a predetermined pattern having a plurality of vacant areas, and forming a dielectric layer above the patterned metal layer, filling the vacant areas in the patterned metal layer. A bond pad is then formed on the dielectric layer above the patterned metal layer.
In one aspect of the invention, the reinforcing patterned structure may be a joined or interconnected structure. In another aspect of the invention, the reinforcing patterned structure may comprise disjoined or non-interconnected and repeating elements.
A technical advantage of the present invention is the improved structural integrity of bond pads so that forces exerted during bonding and probing do not damage the bond pad and underlying structures. These technical advantages are possible without changing bonding or probing parameters, which may decrease process throughput. The result is a more reliable integrated circuit and decreasing bonding failures.